Magneto-Transport Characteristics of Magnetic Tunnel Junction With a Synthetic Antiferromagnetic Amorphous CoFeSiB Free Layer

Abstract

A synthetic antiferromagnet (SAF) structure comprising two ferromagnetic amorphous CoFeSiB layers was employed as a free layer in magnetic tunnel junctions (MTJs) to enhance magnetotransport and magnetization switching performance. In Si-SiO2/Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlOx 1.5/CoFeSiB t(t= 3.5, 4.0,4.5, 5.0)/Ru 1.0/CoFeSiB 7-t/Ru 60 (nm) MTJ structures, the tunneling magnetoresistance (TMR) ratio, interlayer coupling field, and switching field all showed layer thickness dependence for 3.5 mn <= t <= 5 nm. When the CoFeSiB t layer (a lower ferromagnetic layer in the SAF structure) became thinner, a lower TMR ratio with a lower switching field was observed. Whereas, when the CoFeSiB t layer became thicker, a higher junction resistance with a lower interlayer coupling field was observed. This was resulted from the decrement of saturation magnetization and the smooth tunnel barrier/free-layer interface formation, respectively.